Because shrinking up makes no sense

In an attempt to explain the phenomenon of incredible shrinking drinks, the editors on the Yahoo! front page, make sure you understand that the drinks have been shrunk down, and not shrunk up:

If you think that means a half gallon of milk is now just 60 ounces, or a pint of cream is 12 ounces, you would be wrong. The actual shrinking of drinks is a myth. Instead, some large sizes of some drinks have been banned in New York City. No shrinkage was involved in the ban.